Non-reciprocal devices, such as isolators, circulators and phase shifters, are important in electrical systems, such as communication networks, to prevent adverse backward reflection, interference and feedback. Traditionally, non-reciprocity in microwaves and optics is achieved by using magneto-optical materials, where non-reciprocity is the result of biasing with a static magnetic field. By requiring the use of a static magnetic field, heavy and bulky magnets are required which are difficult to integrate in the non-reciprocal devices. As a result, different biasing schemes have been devised in an attempt to eliminate the use of heavy and bulky magnets.
One such scheme involves the use of metamaterials based on transistor-loaded ring resonators that are biased via direct current. Unfortunately, such a scheme involves significant power consumption (power consumption in the biasing network and the transistor itself) and its operation is limited to microwave frequencies.
Another scheme involves the use of optical isolators consisting of spatially-temporarily modulated waveguides that are biased via linear momentum. Unfortunately, such a scheme is limited to specific applications where the spatially-temporarily modulated waveguides need to be many wavelengths long. Furthermore, such a scheme also involves significant power consumption in the biasing network.